Composite polyamide reverse-osmosis (RO) membranes are known. See, for example, U.S. Pat. Nos. 4,259,183, 4,529,646, and 4,277,344. The treatment of such membranes to increase rejection has been described, for example, in U.S. Pat. No. 4,960,517, which discloses a process whereby a cross-linked polyamide RO membrane is treated with a solution of an amine-reactive reagent group such as the sodium salt of chloracetic acid, a carboxylic acid anhydride, a carboxylic acid ester, a 1,3-heterocyclic sultone, and an amine-reactive ethylenically unsaturated compound such as acrylic acid. The resulting membrane has an improved rejection for solutes such as NaCl, NaNO.sub.3, H.sub.2 SO.sub.4, NaOH, and isopropyl alcohol (IPA). U.S. Pat. No. 4,960,518 describes a method of treating a polyamide RO membrane with an oxidizing agent such as peroxycarboxylic acid, periodic acid, chloramine compounds, and N-bromoamine to improve its rejection of sulfuric acid and IPA. U.S. Pat. No. 4,964,998 describes a process for separating water from organics such as IPA wherein the permselective layer of the RO membrane is a cross-linked polyamide that has been treated with an amine-reactive reagent such as sultone or nitrous acid. Because such membranes are often used in the treatment of chlorinated water, there has been a general recognition in the art of a need for such membranes to have a high resistance to attack by chlorine. Various methods have been proposed to improve the chlorine resistance of composite RO membranes. See, for example, U.S. Pat. No. 4,812,238.
Thus, although the prior art has utilized various treatments of polyamide RO membranes to improve their chlorine-resistance and their rejection of organics, there has been no recognition of the use of an acyl halide treatment to so improve such membranes. There is therefore a need in the art for membranes capable of simple fabrication that have high rejections for organic compounds and improved chlorine resistance.